1. Field of the Invention
The present invention relates to systems and methods for separating and concentrating cells, e.g., regenerative cells, from a wide variety of tissues. The present invention particularly relates to automated systems and methods for separating and concentrating regenerative cells, e.g., stem cells and/or progenitor cells, from adipose tissue.
2. Description of Related Art
Regenerative medicine harnesses, in a clinically targeted manner, the ability of regenerative cells, e.g., stem cells and/or progenitor cells (i.e., the unspecialized master cells of the body), to renew themselves indefinitely and develop into mature specialized cells. Stem cells are found in embryos during early stages of development, in fetal tissue and in some adult organs and tissue (Pera et al., 2000). Embryonic stem cells (hereinafter referred to as “ESCs”) are known to become many if not all of the cell and tissue types of the body. ESCs not only contain all the genetic information of the individual but also contain the nascent capacity to become any of the 200+ cells and tissues of the body. Thus, these cells have tremendous potential for regenerative medicine. For example, ESCs can be grown into specific tissues such as heart, lung or kidney which could then be used to repair damaged and diseased organs (Assady et al., 2001; Jacobson et al., 2001; Odorico et al., 2001). However, ESC derived tissues have clinical limitations. Since ESCs are necessarily derived from another individual, i.e., an embryo, there is a risk that the recipient's immune system will reject the new biological material. Although immunosuppressive drugs to prevent such rejection are available, such drugs are also known to block desirable immune responses such as those against bacterial infections and viruses. Moreover, the ethical debate over the source of ESCs, i.e., embryos, is well-chronicled and presents an additional and, perhaps, insurmountable obstacle for the foreseeable future.
Adult stem cells (hereinafter interchangeably referred to as “ASCs”) represent an alternative to the use of ESCs. ASCs reside quietly in many non-embryonic tissues, presumably waiting to respond to trauma or other destructive disease processes so that they can heal the injured tissue (Arvidsson et al., 2002; Bonner-Weir and Sharma, 2002; Clarke and Frisen, 2001; Crosby and Strain, 2001; Jiang et al., 2002a). Notably, emerging scientific evidence indicates that each individual carries a pool of ASCs that may share with ESCs the ability to become many if not all types of cells and tissues (Young et al., 2001; Jiang et al., 2002a; Jiang et al., 2002b; Schwartz et al., 2002). Thus, ASCs, like ESCs, have tremendous potential for clinical applications of regenerative medicine.
ASC populations have been shown to be present in one or more of bone marrow, skin, muscle, liver and brain (Jiang et al., 2002b; Alison, 1998; Crosby and Strain, 2001). However, the frequency of ASCs in these tissues is low. For example, mesenchymal stem cell frequency in bone marrow is estimated at between 1 in 100,000 and 1 in 1,000,000 nucleated cells (D'Ippolito et al., 1999; Banfi et al., 2001; Falla et al., 1993). Similarly, extraction of ASCs from skin involves a complicated series of cell culture steps over several weeks (Toma et al., 2001) and clinical application of skeletal muscle-derived ASCs requires a two to three week culture phase (Hagege et al., 2003). Thus, any proposed clinical application of ASCs from such tissues requires increasing cell number, purity, and maturity by processes of cell purification and cell culture.
Although cell culture steps may provide increased cell number, purity, and maturity, they do so at a cost. This cost can include one or more of the following technical difficulties: loss of cell function due to cell aging, loss of potentially useful non-stem cell populations, delays in potential application of cells to patients, increased monetary cost, and increased risk of contamination of cells with environmental microorganisms during culture. Recent studies examining the therapeutic effects of bone-marrow derived ASCs have used essentially whole marrow to circumvent the problems associated with cell culturing (Horwitz et al., 2001; Orlic et al., 2001; Stamm et al., 2003; Strauer et al., 2002). The clinical benefits, however, have been suboptimal, an outcome almost certainly related to the limited ASC dose and purity inherently available in bone marrow.
Recently, adipose tissue has been shown to be a source of ASCs (Zuk et al., 2001; Zuk et al., 2002). Unlike marrow, skin, muscle, liver and brain, adipose tissue is comparably easy to harvest in relatively large amounts (Commons et al., 2001; Katz et al., 2001b). Furthermore, adipose derived ASCs have been shown to possess the ability to generate multiple tissues in vitro, including bone, fat, cartilage, and muscle (Ashjian et al., 2003; Mizuno et al., 2002; Zuk et al., 2001; Zuk et al., 2002). Thus, adipose tissue presents an optimal source for ASCs for use in regenerative medicine.
Suitable methods for harvesting adipose derived ASCs, however, may be lacking in the art. Existing methods may suffer from a number of shortcomings. For example, the existing methods may lack the ability to optimally accommodate an aspiration device for removal of adipose tissue. The existing methods may also lack partial or full automation from the harvesting of adipose tissue phase through the processing of tissue phases (Katz et al., 2001a) and/or. The existing methods further may lack volume capacity greater than 100 ml of adipose tissue. The existing methods may yet further lack a partially or completely closed system from the harvesting of adipose tissue phase through the processing of tissue phases. Finally, the existing methods may lack disposability of components to attenuate concomitant risks of cross-contamination of material from one sample to another. In summary, the many prior art methods for harvesting ASCs from adipose tissue do not appear to overcome the technical difficulties associated with harvesting ASCs from skin, muscle, liver and brain described above.
Accordingly, there remains a need in the art for systems and methods that are capable of harvesting regenerative cell populations, e.g., ASCs, with increased yield, consistency and/or purity and of doing so rapidly and reliably with a diminished or non-existent need for post-extraction manipulation. Ideally, such a device, system or method would yield regenerative cells in a manner suitable for direct placement into a recipient.